The present invention relates to an electrochromic display device (referred to as ECD hereinafter) and more particularly, to ECD of the type in which at least two discrete electrochromic materials (one of which is referred to as "EC material" hereinafter) are layered so that the two EC materials provide a visual display in combination.
The present invention is concerned with ECD of the type which comprises a first EC material layer, a second EC material layer, and a solid electrolyte layer interposed between the first and the second EC material layers. Either of the first and the second EC material layers can function as a display electrode and a counter electrode. Preferably, the first EC material layer is made of a material for coloring upon oxidation (referred to as an "oxidation-coloring material") and the second EC material layer is made of another material for coloring upon reduction (referred to a "reduction-coloring type").
Upon the application of a current having a single direction, the first and the second EC material layers are colored simultaneously. No background layer is interposed between them, so that the color by the first EC material layer is mixed with that by the second EL material layer. The display contrast can be improved by this mixture of the colors. When the reverse current is applied to the first and the second EL material layers, they are decolored simultaneously.
According to the conventional manufacture method for the above type of ECD, each of the first and the second EL material layers, the solid electrolyte layer and an insulating layer must be patterned using a mask evaporation or etching process in discrete steps, which was very complicated.
Very minute exact pattern alignment is required between the four layers. If one layer of the first and the second EC material layers, and the solid electrolyte layer is misaligned with respect to the other, the response time of the deviated portion of the layer is very slow, to thereby damage the display visibility. Since the insulating layer is provided for preventing the leakage between the EC material layers, the insulating layer must be deposited to completely cover portions free of the EC material layers, and the solid electrolyte layer.